Method of making a powder dispensing cylinder for an electrostatic powder fixing device

ABSTRACT

THE PRESENT INVENTION RELATES TO AN ELECTROSTATIC POWDER IMAGE PRINTING SYSTEM, MORE PARTICULARLY, TO A MAGNETIC CYLINDER FOR UNIFORMLY DISPENSING TONER POWDER IN A POWDER IMAGE FIXING DEVICE.

1971 w. KNECHTEL 3,553,832 METHOD OF MAKING A POWDER DISPENSING CYLINDERFOR AN ELECTROSTATIC POWDER FIXING DEVICE Original Filed Jan. 16, 1967\NVENTCR WILHELM KNECHTEL MTOHNLY United States Patent Int. Cl. H01f7/06 U.S. Cl. 29-607 1 Claim ABSTRACT OF THE DISCLOSURE The presentinvention relates to an electrostatic powder image printing system, moreparticularly, to a magnetic cylinder for uniformly dispensing tonerpowder in a powder image fixing device.

This application is a division of application No. 609,386, filed Jan.16, 1967, now Pat. No. 3,464,383.

In the'usual and well known form of an electrostatic printing system, aradiation image of the copy to be reproduced is projected onto thesensitized surface of a plate to form an electrostatic latent imagethereon. Subsequently, the latent image is developed with an oppositelycharged developing material to form an electrostatic powder imagecorresponding to the latent image on the plate surface. The powder imageis then electrostatically transferred to a paper web upon which theimage is affixed by a fixing device. As a result, the powder image ispermanently adhered to the paper web.

The fixing device essentially comprises a toner powder which is anelectrostatically charged, finely divided material, such as anelectroscopic powder. Various arrangements have been devised fordispensing the toner powder onto the paper web to fix the image thereon.A common form of a powder dispenser comprises a cylinder which contactsboth the paper web and the toner powder to distribute the powder on theweb. However, it has been found that the powder will be non-uniformlydeposited upon the moving paper web if the powder was not initiallyuniformly distributed on the surface of the cylinder. Therefore,numerous attempts have been made to deposit the powder as uniformly aspossible on the cylinder surface.

In a proposed cylinder construction, the cylinder itself constituted anindependent magnetic pole and has positioned adjacent to it a secondmagnetic pole of opposite polarity so that the lines of magnetic fluxbetween the two poles will extend radially of the cylinder along theentire length thereof. While a uniform distribution of powder has beenachieved with such a construction, it has been found that such anarrangement is expensive to construct and requires considerablyincreased overall dimensions of the apparatus. 7

It has therefore been proposed to construct the cylinder itself in theform of a permanent magnet with the lines of flux extending in or nearthe surface of the cylinder. In this cylinder, local accumulations ofthe powder on the surface of the cylinder resulted in a non-uniformdistribution of the powder upon the traveling paper web. In an attemptto avoid this difficulty the cylinder was rotated at a peripheral speedgreater than the speed of the traveling paper web. However, thisincreased rotation of the cylinder did not completely eliminate thisdifficulty since if the cylinder rotated too rapidly the powder would bereleased as a dust which would then settle on the paper web even inthose areas which were not electrostatically charged. When the cylinderwas rotated relatively slower, the powder would appear as longitudinal"ice bands along the cylinder or as transverse bands across the paperweb.

It was further proposed to construct such a cylinder of individualmagnet disks which were inclined to the axis of rotation of thecylinder. Thus, when the cylinder rotated the magnetic field would bemoved across the traveling paper web parallel to the axis of rotation.This proposal was unsatisfactory in that while longitudinal bands wereeliminated from the paper web undulating bands were formed in theirstead.

It is therefore the principal object of the present invention to providea novel and improved magnetic powder dispensing cylinder for anelectrostatic powder fixing dev1ce.

It is another object of the present invention to provide such a magneticcylinder having a uniform magnetic field upon the peripheral surfacethereof.

It is an additional object of the present invention to provide amagnetic cylinder which will uniformly dispense toner powder upon atraveling web without any dust-like diffusion of the powder.

In one aspect of the present invention there is provided a magneticcylinder wherein the north and south magnetic poles extend along theperipheral surface of the cylinder. A plurality of circumferentiallyundulating alternately spaced north and south pole magnetic elements arepositioned on the peripheral surface of the cylindrical member. Theundulations of the north and south pole elements correspond so that aplurality of closely spaced adjacent pairs of north and south poles aredefined along the peripheral surface of the cylindrical member. Themagnetic elements may either be circular or helical.

In one embodiment of the invention a plurality of aligned magnetic disksmade of magnetic rubber are stacked to form a cylinder with the disksbeing of alternate north and south polarity. Pre-formed steel disks maybe interposed between the magnetic disks.

In another embodiment of the invention a layer of magnetic rubber ispositioned about a cylindrical core. The magnetic rubber is thenmagnetized to form a plurality of closely spaced undulating north andsouth magnetic elements along the peripheral surface of the cylinder.

Other objects and advantages of the present invention will be apparentupon reference to the accompanying description when taken in conjunctionwith the following drawings wherein;

FIG. 1 is an elevational view of a portion of the magnetic cylinderaccording to the present invention and showing the circumferentiallyextending magnetic pole elements;

FIG. 2 is a perspective piew of a disk used in the construction of thepresent invention;

FIG. 3 is a view similar to that of FIG. 1 but in enlarged scale andshowing the polar elements together with the magnetic lines of forceestablished by these elements;

FIG. 4 is a view similar to that of FIG. 1 but showing anotherembodiment of the present invention wherein magnetic rubber ispositioned over a cylindrical core; and

FIG. 5 is a transverse sectional view of the magnetic cylinderillustrated in FIG. 4.

Proceeding next to the drawings wherein like reference symbols indicatethe same parts throughout the various views a specific embodiment andmodifications of the present invention will be described in detail.

As may be seen in FIGS. 1 and 2 a plurality of steel disks 1, asillustrated in FIG. 2, and a plurality of magnetic disks 2 arealternately aligned as shown in FIG. 1 to form a magnetic cylinder 3.The steel disks 1 have their periphery corrugated with the magneticdisks 2 also being corrugated. If desired the magnetic disks may merelybe flat disks of magnetic rubber, a suitable synthetic resin or thelike, which are flexed into the proper position when the plurality ofpre-formed steel disks are compressed to form the cylinder.

The magnetic rubber disks 2 provide the magnetic flux distribution asshown in FIG. 3. The distribution of the magnetic flux may be seen alongthe lower portion of the cylinder 3 shown in FIG. 3. It will be apparentthat with this construction of the magnetic cylinder there will be auniform distribution of the magnetic field along the entire length ofthe cylinder. As a result, the toner powder will become depositeduniformly over the entire peripheral surface of the magnetic cylinder.

During rotation of the cylinder any irregularities in the thickness ofthe layer of powder on the cylinder will be quickly smoothed out by theback and forth movement of the magnetic field in the axial direction. Aa result, the picture that is to be developed and fixed will besubjected to a uniform deposition of powder.

The positioning of the steel disks between the magnetic disks in theassembly of the magnetic cylinder will enable the magnetic lines offorce to pass outwardly from the surface of the cylinder in the manneras schematically illustrated in FIG. 3.

The assembly of the pre-formed steel disks and magnetic rubber disks inthis manner will form a magnetic cylinder having a cylindrical outersurface but with magnetic polar elements defining circumferentiallyundulating paths about the peripheral surface of the cylinder. Thesepaths of the magnetic elements are substantially circular but it ispointed out that these paths may be made helical in shape.

A further embodiment of the present invention is illustrated in FIGS. 4and 5. In this embodiment there is provided a cylindrical core 10 overwhich a cylinder of magnetic rubber 11 is fitted to form the cylinderindicated generally at 15. After assembly, the rubber cylinder 11 isthen magnetized so that pairs of magnetic elements 12 and 13 will beformed as illustrated in FIG. 4. The distribution of the magnetic linesof force from this arrangement of the magnetic polar elements will bethe same as illustrated in FIG. 3.

In a further modification, the magnetic disk elements may be formed froma thermoplastic material into the shapes as shown for the steel disk inFIG. 2. A plurality of these preformed plastic elements are thenassembled to form the cylinder.

A simple but effective method for carrying out the magnitization of thecylinder illustrated in FIGS. 4 and 5 will next be described. A pair ofspaced electrically conducting wires are helically wound about the outersurface of the magnetic cylinder 11. These wires are undulated orcorrugated into substantially the shape as shown in FIG. 4. The ends ofthe wires are then connected and direct current passed through thewires. The result will be to define a plurality of circumferentialundulating magnetic members along the peripheral surface of thecylinder.

Thus it can be seen that the present invention provides a magneticcylinder wherein the north and south magnetic poles are arrangedannularly or helically or the like about the peripheral surface of thecylinder in an undulating manner. The north pole elements are arrangedin contiguous pairs alternately with contiguous pairs of south poleelements. The resulting arrangement of north and south pole magneticelements provide a uniform distribution of magnetic flux along theentire peripheral surface of the cylinder. As a result the toner powderwill adhere to the peripheral surface of the magnetic cylinder in auniform layer. The uniform distribution of the toner powder on themagnetic cylinder will enable the toner powder to be uniformly dispensedupon a moving paper web to fix the image thereon.

It will be understood that this invention is susceptible to modificationin order to adapt it to different usages and conditions and,accordingly, it is desired to comprehend such modifications within thisinvention as may fall within the scope of the appended claim.

Iclaim:

1. In a process for making a powder dispensing cylinder for anelectrostatic powder image fixing device with the cylinder havingcircumferentially undulating alternatingly spaced north and south polemagnetic elements on the periphery thereof, the steps of applying alayer of magnetic rubber upon a cylindrical core member, winding a pairof spaced electrically conducting wire helically around the outersurface of the layer of magnetic rubber, connecting together one pair ofends of said Wires, and passing a direct current through said wires.

References Cited UNITED STATES PATENTS 3,098,765 7/1963 Keller et al.1l8-637 3,213,335 10/1965 Bourne 335-303 3,229,030 1/1966 Baermann335303X 3,392,432 7/1968 Naumann ll8-637X JOHN F. CAMPBELL, PrimaryExaminer C. E. HALL, Assistant Examiner US. Cl. X.R.

